1. Field of the Invention
The present invention generally relates to a method for automatically measuring pupillary distance (PD), and more particularly, the present invention relates to an automatic pupillary distance (PD) measurement system and a PD measuring method having capability to automatically check to detect if a measured object moves into an adequate measuring position and automatically guide the user for obtaining a correct head posture for pupillary distance (PD) measurement.
2. Description of the Related Art
Nowadays, due to the improvements in the digital technologies with the increased demand in the current marketplace for reliable automated credit card processing systems capable for handling financial transactions for customers. One possible application or usage scenario for automated credit card processing system can involve a customer purchasing a pair of glasses and paying for the purchase of the pair of glasses by holding a credit card in his hand, and directing a camera on the hand-hold device or PC for image capture of him holding the credit card, for extracting the credit card's edges as reference length (credit card has international standard width 85.6 mm) for performing a pupillary distance (PD) measurement. Meanwhile, people have recognized that automatic extraction of (eye) pupils' features and the card edges of the credit card for various users under different environments using computer vision technology today can lead to many issues and difficulties. Therefore, almost only manual vision-assisted operation systems are currently available in the marketplace today. For example, traditional manual pupillary distance (PD) measurement process includes the following steps. Step 1: As shown in FIG. 1a, a black band of the credit card undergoes adjustment by moving a mouse cursor inside a black band region of the credit card and click the mouse to identify the black band region; and visually and manually adjusting a card edge of the credit card to fit the edge of the card band in the captured photo image. Step 2: As shown in FIG. 1b, a pupil center undergoes adjustment by visually and manually moving a mouse cursor up/down to adjust an alignment frame to align with a vertical position of the pupils, and similarly, visually and manually moving the mouse cursor left/right to adjust the alignment frame to align with a horizontal position of the pupils, and then followed by obtaining a pupillary distance value. Repeatability requirement of visual detection and measurement results for the pupil distance is typically beyond manual adjustment capability (measurement error should be within 2 mm) due to contributions and influence of differences found in various human postures and operating distances relative to the camera. Therefore, the traditional manual visual detection and measurement system needs to have a smart UI to guide the user to come into or arrive at a reasonable measuring range to maintain consistent measuring condition for measuring pupil distance.
In a first usage scenario of the traditional manual pupillary distance (PD) measurement process, as shown in FIGS. 2a, 2b, and 2c, the measurement results for the pupil distance for a same user located at a same measurement distance from the camera would vary accordingly with different head postures. Therefore, even with the pupil distance being measured at the same measurement distance from the camera, the unsatisfactory or inadequate measurement accuracy of the pupil distance caused by differences in various head postures can be seen or determined. As shown in FIG. 2a, the pitch angle of the head of the person in the illustrated image is less than 0, and the pupil distance is measured to be 65.8 mm. As shown in FIG. 2b, the pitch angle of the head of the person in the illustrated image is equal to 0, and the pupil distance is measured to be 63.4 mm. Referring to FIG. 2c, the pitch angle of the head of the person in the illustrated image is greater than 0, and the pupil distance is measured to be 61.0 mm. Therefore, it is evident that at different head pitch angles, the pupil distance measurement results being obtained between 61.0 mm to 65.8 mm, are therefore not very precise or consistent.
In a second usage scenario of the traditional manual pupillary distance (PD) measurement process, as shown in FIGS. 3a, 3b, and 3c, the measurement results for the pupil distance for the same user having the same head posture would vary accordingly under different measurement distances of the head to the camera. In other words, even with the same head posture, the pupil distance measurement results of the same user would still vary (quite a bit) when being configured at different measurement distances relative to the camera. Therefore, even with the same head posture, the insufficient measurement accuracy of the pupil distance obtained by the traditional manual pupillary distance (PD) measurement process caused by differences in various measuring distances of the head can be seen. Referring to FIG. 3a, a closest measurement distance from the camera of the head of the person in an illustrated image is provided, and the pupil distance is measured to be 61.4 mm. In a second actual experiment performed by inventor as shown in FIG. 3b, a normal measurement distance (at a typical or average distance) of the head of the person from the camera in the illustrated image is provided, and the pupil distance is measured to be 62.6 mm. Referring to FIG. 3c in a third actual experiment performed by inventor, a farthest measurement distance from the camera of the head of the person in the illustrated image is provided, and the pupil distance is measured to be 64.3 mm. Therefore, it is evident that at different measurement distances of the head from the camera, the pupil distance measurement results being obtained ranged between 61.4 mm to 64.3 mm, are therefore are not very precise or consistent.
Thus, the drawbacks of the traditional manual pupillary distance measurement system as exemplified by examples and usage scenarios described above are as follow: (1) there lacks a proper constrain nor guidance from an UI design for the user to take photos with a front view and place the credit card on a face region properly; (2) there lacks a proper constrain or guidance from the UI design for the user to guide him to maintain a correct head posture and a correct measurement distance during the pupil distance measurement; (3) pupillary distance measurement requires of too many manual operation steps (such as in the form of mouse cursor moving and clicking) are needed to complete the pupil distance measurement process. Therefore, the entire pupil distance measurement process is inconvenient and may be prone to produce pupil distance measurement errors. In other words, disadvantages of conventional pupillary distance (PD) measuring system include for example, being more complicated to use, providing insufficient pupillary distance (PD) measurement accuracy, and achieving unsatisfactory overall user usage experience. Therefore, there is room for improvement in the related art.